This invention relates to a droplet ejecting head which heats a viscous fluid with heating elements to produce bubbles that cause the fluid to be ejected as droplets.
One of the inkjet printers that have become popular today are of a type that uses a thermal inkjet printer head in which part of ink is abruptly heated to form a bubble in the ink and ink droplets are propelled and ejected by the expansion force of the bubbles formed in the ink. With this type of ink jet printers, high quality image can be easily printed on recording paper. However, the recording paper for use in printing is mainly of dedicated type which is comparatively expensive and if plain paper having fairly high water absorbency is used, ink that has struck the surface of the paper will blot there, making it occasionally impossible to print high quality image.
In order to solve this problem, one may think of employing ink of comparatively high viscosity so that it will not blot even if it is printed on plain paper but then it becomes necessary to ensure accurate ejection of the highly viscous ink. JP 11-10878 A and JP 9-327918 A propose inkjet printer heads that employ ink of high viscosity.
The inkjet printer head disclosed in JP 11-10878 A comprises an ejection port through which ink is ejected, a first heating element which is provided in association with the ejection port and which heats the ink to form a bubble that ejects it, and a second heating element that is adjacent to the first heating element and which is dedicated to heating the ink. Because of such construction, JP 11-10878 A says, ink of high viscosity can be rendered less viscous by heating so that high refill characteristics are realized with high efficiency and meniscus is sufficiently stabilized to provide improved print quality.
The fluid ejecting head disclosed in JP 9-327918 A is characterized by providing a moving member that faces a foaming region where a bubble is to be formed so that the two fluid channels spaced apart by the moving member will have different internal pressures. A foaming fluid that is to form a bubble and an ejection fluid that is to be ejected as a droplet are supplied into separate fluid channels and the bubble formed in the foaming fluid moves the moving member, causing the ejection fluid to be ejected. Because of this design, JP 9-327918 A says, ink of high viscosity can be supplied in a consistent manner and the fluid that forms a bubble can be refilled with higher efficiency.
However, the inkjet printer head disclosed in JP 11-10878 A suffers the problem of being costly since it has at least two heating elements. What is more, the use of plural heating elements is susceptible to defects and the service life of the head is prone to be shortened.
The fluid ejecting head disclosed in JP 9-327918 A has two fluid channels spaced apart by the moving member and they are adapted to have different internal pressures. This complicates the structure of the head, not only shortening its service life but also increasing the production cost.